Update pytest log printing option

[LaikaN57]

Issue #, if available:
The following warning is generated when running cfn test:

================================================================= warnings summary ==================================================================
.venv/lib/python3.7/site-packages/_pytest/logging.py:499
  .venv/lib/python3.7/site-packages/_pytest/logging.py:499: PytestDeprecationWarning: --no-print-logs is deprecated and scheduled for removal in pytest 6.0.
  Please use --show-capture instead.
    _issue_warning_captured(NO_PRINT_LOGS, self._config.hook, stacklevel=2)

Description of changes:
Migrate to new pytest option to resolve warning.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[LaikaN57]

And just for reference, here is my env which results in pytest==5.4.3 currently:

aws-sam-cli==0.53.0
awscli==1.18.86
black
boto3==1.14.9
botocore==1.17.9
#cloudformation-cli>0.1.4
cloudformation-cli @ git+https://github.com/aws-cloudformation/cloudformation-cli.git@85dba80439e044f65e294af65d36fa0934151bad
cloudformation-cli-python-lib==2.0.0
cloudformation-cli-python-plugin==2.0.0
docker==3.7.3
logmatic-python==0.1.7

[PatMyron]

pytest 6.0 released this week, so --no-print-logs is getting more urgent to fix, especially since we required 6.0+ for next release

[ammokhov]

pytest 6.0 released this week, so this is getting more urgent to fix, especially since we required it for next release

bumped the dependency here #518

[ammokhov]

good change, thank you